I did allot of testing to find the ideal prop for my model aircraft motors. Convention dictates a certain pitch for modelers to use, most commonly an 8-10 inch per rotation prop is used. I tested with the 12-8 and found the engine could not drive the prop into the power band of the 2 stroke motors being used, it would stall the engine and less thrust was produced. My experiments lead me to a larger prop and a shorter pitch. My 10 cc motors could drive a 13-4 wide blade into the 12,000-12,500 rpm range, the motor was happier and the thrust was twice the thrust produced by the 12-8 prop. It pays to do the testing, never listen to idiots, always do the testing yourself.
I had two props on an old outboard motor many years ago. They were the exact same make, diameter and pitch. One was cupped slightly different and the motor performed noticeably better with one over the other.
Excellent Talk, although I clean barnacles & oysters for a living as a hull diver. Alot of the over engineering equals extra growth and extra drag do to marine growth. I am seeing alot more IPS Drives that eliminate bow and stern thrusters and also give the ability for joystick controls. The propeller design seems to come to mind because of this talk. It is a pod drive with forward facing twin propellers rotating opposite one another, forward propeller having three blades and aft propeller having 4 blades. It probably maximizes thrust while countering swirling. This is all just from underwater observation though, no real performance testing by me.
Most people confuse propeller shape - especially the leading edge dimension - with air and low / high pressure of air. Water is incompressible so it is about how a prop redirects water flow around it and thrust is developed by the change of water flow over speed and water pressure after it leaves the propeller. So blunt leading edges are no longer used much anymore. Very surprised you did not cover gear ratio selections and the importance that props spin slowly ... because fast spinning props cause cavitation at the tip and lose thrust. Another missing element is Blade Area ratio. Very important, and number of blades and blade shape. To the question below Impellers are not more efficient than propellers, because they are inherently different to propellers, as impellers are part of pumps. counter rotating props could also be discussed here regarding flow efficiencies. And speed limitations. For standard propellers max speed is around 37kts in most cases. This can be improved if CCP props are used - also known as variable pitch propellers and for very high speeds props become wedges so they become supercavitating foils and are raised for planing craft so become surface props and are good to very high speeds.
Three important unmentioned items: 1) Propeller swirl is caused by a propellers inability to draw water into it by gravity equal to the exhaust velocity volume of the propeller . The exhaust volume exactly equals the intake. A delay causes most of the swirl. 2) Marine propellers get the water from the surface. The reason for this is the momentum of water. due to its mass. If not true, a marine propeller would be pulling water from China. 3) Propellers are very sensitive to tip speed. A 20 inch 4 blade propeller with 0 pitch has @ 1000 rpm, a tip speed of 5233 feet/minute, or just under the old "Mile a Minute" rule in engineering. The power needed is 5 HP.. The same 20 inch 4 blade prop with 0 pitch , at 2000 rpm requires 40 HP. This is why reduction gears help with thrust AND SPEED. The optimal diameter/pitch ratio is 12/10 for line pull and 10/12 for speed. This works from a practical standpoint. Usually, for a general purpos boat, a square wheel is optimal. ,All of this information is based on design of several boats and variations in design. Hope it helps someone. Especially hope it helps someone involved in using finite analysis or other digital development software HINT...HINT.
Interesting points. Myself, I believe in scientific tests and hard experiments. It would be really fun to check these concepts. Based on your description, your first point seems to indicate that propeller swirl is due to an interaction with gravity. If that was the case, we could easily create a test rig with the propeller mounter horizontal instead of the conventional vertical. Gravity would be equal across the entire propeller. According to what you described, we should get no swirl in that case. I can also think of another test for the argument that propellers get their water from the surface. Simply stick the propeller in a pipe and ensure the inlet to the pipe is well below the surface. If the propeller truly gets it water from the surface, eventually, the propeller should run out of water, or the flow through the propeller should just stop. It would be fun to test.
This is good stuff. As a recreational boater (power, sail, rowing, (as well as a huge fan of land/ice sailing)) I’m hoping you can address some items that pertain to smaller vessels
Yes, absolutely. I'm not an expert in propeller noise, but some of the basic design principles include: - always use an odd number of blades to reduce pressure pulses as blades rotate past vertical surfaces. (even number of blades, and two blades align at the same time, doubling the pressure pulse). - Increase the number of blades to reduce cavitation and general noise from the propeller - If possible, rotate at slower RPM.
I like the sense of humour of defining the most efficient propeller, as one which has zero angles of attack and no thrust! Here is a question that one never seems to see the answer to it. Considering that water is incompressible and the air is compressible, then if we take the same multiblade propeller with a high blade area for comparison, ( even an impeller) what would the velocity/pressure profile of the fluid medium being used ( compressible air or incompressible water) THROUGH THE THICKNESS OF THE PROPELLER BETWEEN THE BLADES. and the immediate zone around the propeller. It is not an easy answer especially for those water propellers where the water velocity changes as it goes through and accelerates through the propeller!!!
As you said, predicting the exact velocity profile is a little difficult (but achievable with modern computers). Interesting, the theory and mathematics behind propellers started with this exact problem. We started with a goal for a velocity and pressure profile and created a device to achieve that. In the zone directly around the propeller blades, we see minimal change in velocity of the fluid. The one exception is the fluid right on the surface of the blades, which accelerates as it passes around the leading edge of the blade. The pressure shows a huge change in the region around the blades. It spikes from a strong negative pressure (suction on the forward face) to a strong positive pressure (pushing on the back face). This is the key behind propellers. We are trying to create a sharp change in pressure, and the velocity change is just an unfortunate side effect. The velocity of the fluid accelerates as it approaches the propeller and then slowly decelerates far downstream.
@@DatawaveMarineSolutions Thank you for replying. I thought about writing a book on propellers as I do feel that propellers could be misunderstood. I wish to share my philosophy on some types of propellers/ impellers. The philosophy stems from the fact that water is incompressible and it is also non-expandable as we must stay away from cavitation in this discussion. Having a propeller whose blades are very thin and they form what is effectively a multi-start thread on a deeply threaded rod, we can forget about Bernoulli coming into the picture, as there are other features to consider when we know that water is incompressible and non-expandable and is going through a threaded rod where the void spaces remain constant through the threaded rod. If we consider a shrouded impeller, rotating with its helical blades, it is no different from considering a piston moving along a cylinder where it sucks in water from the front and pushes water at the back. WITH SUCH A SITUATION THERE IS NO LINEAR ACCELERATION OF WATER IN BETWEEN THE BLADES OF THE IMPELLER AND SO NO FORCES ARE PRODUCED IN THE SPACE OF THE IMPELLER. However, the non-expandable water at the front of the impeller will cause a sudden suction and the lower pressure than ambient will accelerate water ahead of the impeller. At the other pushing end, the pressure is higher than ambient and so water will pass through the blades at constant velocity but at the pushing end, the water will be accelerated. Hence the propulsion forces are not produced in between the blades of a helical propeller but much ahead and much behind the propeller. All this is due to the fact that we are assuming perfect helical blades and incompressible and nonexpandable water going through. Note any threaded nut is very happy going along a rotating threaded rod, does not increase nor decrease its volume and hence that is the condition of such a water propeller or an impeller we are considering. The forces in a propeller are generated only where there is the acceleration of water and there is none in between the space of a helical propeller but there is plenty of acceleration in the zone before and after the propeller. Now if the blades are not perfectly helical ( really constant pitch) but are curved to diffuse convergently or divergently as in the case of a jet compressor stage, where the exit velocity is different from the incoming velocity, then the volume of water passing in between the blades acting as a diffuser will have to change the area it passes through and so for a curved blade that does not follow a perfect helix, a shrouded propeller should have the exit area of smaller area than the intake. If we assume that the incoming water into the propeller v, has doubled its velocity to 2v at the exit, due to the curve of the blades, then there is an acceleration of water in between the blades of a propeller, and propulsion forces are generated in between the blades of the propeller. Note that in this case we still do not need Bernoulli and aerodynamic sections as it is all a case of changing the momentum through the blades in this case. Now let us talk about surface propellors, as the manner in which they operate efficiently, is related to what was said above. Now water may be incompressible but it will shatter into small drops if it is accelerated heavily and suddenly. If a paddle hits the surface of the water, the sudden effect will put a lot of force on the paddle but only a few drops of spray will shatter around the space where the water was hit. This is no manner in which to accelerate water either by sudden suction or a sudden pressure as water will show other characteristics. If water was like solid steel balls which do not compress not expand, then all that was said above will still apply but water is not like that, IT CANNOT BE ACCELERATED SUDDENLY. This is the importance of arranging for the apparent entry into the blades to be parallel with the leading edge so that the surface propellor will not just hit the lump of water, but it will load it onto the leading edge of the blade and coax it to accelerate along the blade due to the curve of the blade, and as the lump of mass of water reaches the trailing edge it is released with high velocity and there is no more acceleration behind nor before the surface propeller. It is interesting that the solidity of the water in a surface propeller can change it shape due to the rheology of the water and all that acceleration along the blade must be done smoothly and fairly quickly before the lump of mass of water changes shape in smaller spray with no effective mass to drive!. So my point of discussion is between the two limits of a fully immersed propeller with perfectly helical thin blades where the space between the blades does not change and so there is constant velocity, no accelratio0n but a great pressure change between the intake and the exit., and all the propulsion acceleration forces in such a helical propeller will take place totally ahead and behind the propeller. Such a propeller can be enclosed in a parallel cylindrical shroud. Then there is the non-helical curved blade propeller which accelerates the water along with the blades and hence the output area will have to be less than the entry area. For such a propeller with a slip of 50%, it is interesting how small the curve in the blade should be. With surface propellers introducing the air which is incompressible and expandible, then the lumps of masses of water can be separated and that is the reason the surface blade is curved as it is as water is no longer compressible and non-expandable and it can also roll off the blades if the acceleration on the lumps of water is too slow, on the other hand, one just cannot hit a lump of water suddenly as it breaks into small drops and so THE SMOOTH ACCELERATION OR CHANGE IN VELOCITY ON THE BLADES OF A SURFACE PROPELLER MUST BE SMOOTH TO RETAIN LARGE ENOUGH LUMPS OF WATER BEING ACCELERATED ON THE BLADES TO FINISH UP WITH ENOUGH DRIVING FORCES. In my book, I think I would cover the effect of aeration and cavitation on, the helical propeller along which there is no acceleration, the curved blade propeller along which there is acceleration, and Bernoulli and the air propellers will show the misgivings we all know about. However, for now, I want to delve into the situation that even if the velocity of the water in between the blades of a propeller remains constant and the blades are purely very thin helical blades, shrouded in a cylinder in order to avoid water escaping or incoming through the surface of the shroud, one can have a good propulsion drive without thinking too much on the NASA and Eppler and other cross-section which their variation is velocities and pressures along the surface of the blade. The nature in which the accelerations of water are handled is very important and in surface drives, it is not a case of hitting a lump of water with a cricket bat! It is interesting to start looking at drops of water, as stell ballbearing which does not change shape in all the transactions we activate in propellers, or else as rubber balls where the bat/blade hitting the water drop could change its shape as do most surface propellers as there is air introduced to do the buffering, The fact that it is all inertia, acceleration and the rheology of the water, it makes it all so interesting to understand propellers in a better fashion. If we had to add a nozzle ( diffuser) at the back of a propeller then one needs to build up pressure and one cannot use a propeller with narrow blades as found on an aircraft but one with multiple close blades as in a jet compressor where the high pressure built up cannot escape back through the blades as in a helicopter top rotor or indeed any wing with spaces ahead or behind the edges. Nozzles, are really velocity/pressure modifiers" amplifiers" with no moving parts and are related to diffusers, where high pressure can be changed to high velocity or high velocities can be changed to higher pressures. In ships, we need not worry too much about how it all works, as the modern jet engine says it all, for after all, in a jet engine, what happens between the blades is all that happens in a ramjet due to the fact that it uses compressible fluid like air. A jet engine is really a lot of ramjets in parallel made to rotate to be able to work when the engine is stationary on the ground! The fact that water is incompressible and on occasions boils, so expandible, we need to fully understand what happens in between those water blades with the convergent and divergent diffus4ers that may exist before, through, and behind the propeller. Perhaps understanding diffusers are a better investment than understanding propeller blades on their own. We could have a front diffuser, a hot chamber to boil the water, rather than a propeller and a rear diffuser and the whole engine would be located in the propeller!!!!!! Pity that water is so difficult to work with and its latent heat of boiling it takes too much time relative to it passing between the blades of the propeller. Now that would be a difficult machine/propeller to calculate mathematically !!! Thank you for listening,
@08:21 is a Grim's Vane Wheel, which vanes freely on the shaft in the propeller's propwash. Its blade sections within the driving prop's radii are formed to act like a turbine while the vane wheel's sections at the remaining radii towards its blade tips exceeding the prop's diameter are formed to act like a second prop in the wake of the main prop. That gives the vane wheel's blades a bizarr looking warp. Unfortunately, those Grim Vane Wheels didn't really succeed (e.g. their unnoticed loss during their first operation on QE2 after her big propulsion retrofit at the Lloyd Yard at Bremerhaven), and their application remained sporadic to mainly research vessels (e.g. hydrographic RV GAUSS) and a few container vessels from rhe Bremer Vulkan yard that were built in the mid 80s within ship research projects that were partly funded by the government. The same goes for those wake equalizing fins and ducts (e.g. Schneekluth and Grothues-Spork) that were shown a few frames earlier in the video, and which where sporadically applied on other container vessels from the Bremer Vulkan in the same era. P.S. Just found this reprint from HANSA on Schnekluth WED www.schneekluth.com/wp-content/uploads/2019/03/hansa-about_wed.pdf P.P.S. Here another article about the Schneekluth WED (n.b. of course one should be wary about the promised efficiency gains vs. extra costs and risks; of course ship operators asses the latter a bit differently from their or others' experience) www.schneekluth.com/wp-content/uploads/2019/03/brochure_english.pdf P.P.P.S. Here's a paper by a researcher from the Potsdam Ship Model Basin about wake influencing devices. www.marinepropulsors.com/proceedings/2011/WA3-1_Heinke.pdf P.P.P.P.S. Here are some slides from a talk that gives an overview of propulsion efficiency improving measures by two researchers of the Dutch MARIN ship model towing tank. www.stg-online.org/onTEAM/shipefficiency/programm/PPTdeJong.pdf
I recently saw research at NASA Ames regarding the 'PRANDL wing'. Apparently all wing designs are descended in some way from Prandl's mathematical work of 1925, which established the most efficient wing for a given length. But his 1933 paper demonstrated that wasn't the whole story. The most efficient wing without that constraint is longer and has a very different shape. One of the benefits in an aero application is that the tip vortex disappears. These wings have been shown to be substantially more efficient, as well as quieter, and with the replacement of adverse yaw with proverse yaw they eliminate the need for a tail plane, further increasing efficiency. The efficiency has been shown at NASA to also extend to propeller blade shapes. I'd like to see how this applies to boat and ship propellers.
The "duo props" developed by Volvo claim to have a 30% improvement in effectiveness, 30% more speed at the rpm you normally use. If you get 15 knots at 1800 rpm, by using a duo prop you effectively get 19.5 knots at 1800 rpm. That is the claim at least. There must be something to it though, since cruise ships and ice breakers have started using the system on pods. They wouldn't put them on a cruise ship if they didn't give a measurable benefit to ship operation. Many European based yacht builders have started offering Volvo-Penta pod driven option, which does come with the duo prop. With the twin pods in the back, a bow thruster and the application installed in the controls, push a button on the controls and you have dynamic positioning operating.
Would a ducted propeller be more efficient and use the swirl too? Would make a better skin, like shark or a golfball, the propeller more efficient? Does the number of wings rise efficiency? Are the effects in air and water same or is there other things to consider then density? I wish I had a physics teacher like you in high school.
Hi Andreas. Excellent questions. I'll give you the short answers. Would a ducted propeller be more efficient and use the swirl too? Ducted propellers are more efficient, but not because of the swirl. I need to do a whole video those. A propeller duct is basically a wing wrapped around the propeller. As the water gets sucked into the propeller, it runs over the duct wing and produces extra lift. But we also have extra drag from pulling that duct through the water. The benefits outweigh the drag problem up to a certain speed (around 14 - 18 knots). Then it becomes less efficient. Would make a better skin, like shark or a golfball, the propeller more efficient? It might help some. But only about 2-5% The skin friction on the surface of the blade is a minor part of the total blade drag. We actually get a lot of drag from the lift generated by each blade. (Physics: you can't get anything for free.) Some experiments have examined using those surface textures to improve the lift on the blade. With the right texture, we can keep the water flow attached to the blade surface and use a more aggressive blade shape. But more aggressive is not more efficient. All those interactions are hard to gauge. Normally, we have to just build a model and run an experiment to see what happens. Does the number of wings rise efficiency? Generally, yes. Many of the efficiency penalties depend on how much force we try to squeeze into each blade. More blades / wings means less effort from each blade and better efficiency. Are the effects in air and water same or is there other things to consider then density? Air and water are largely the same, aside from the density. Just three major differences: 1.) Air and water propellers generally run at different speeds. 2.) In water, we also need to worry about the limits of cavitation. czcams.com/video/MyZzhwYMytc/video.html That forms an upper limit to how much thrust we can fit in each blade. 3.) In air, we also worry about compressibility. Air is compressible. It's density changes depending on the pressure. This is how we get sonic booms at the speed of 343 m/s. But even before you hit the sonic boom speed, the air compresses some and we need to adjust the design for it. Great questions.
@@DatawaveMarineSolutions Interesting about the blade number, and as always I understand optimization is done with regards to some variables while leaving other variables fixed. My follow up question about your statement that: more blades leads to better efficiency, would be: is that when fixing the required thrust per blade or in general? Say i would like a certain low speed from a small displacing vessel well below hull speed. The free/undisturbed stream and the propeller diameter are both fixed. Would more propeller blades still be beneficial over fewer when the propeller thrust requirement is constant? Best regards, Christian
I’ve heard of cupping the blades for efficiency, but has anyone done more on blade designs away from the tip and more at the leading and trailing ends to increase efficiency and reduce noise?
That is an excellent question. I can only partially answer it. I know a few professionals that work in small boat prop design, and I suspect they know some secrets about optimizing performance at the propeller hub. That said, I suspect the flare on the hub has a lot to do with the engine exhaust. Most outboards route their exhaust flow through the propeller hub. So we can't put a tapered hub on there. We need an open hub to let the exhaust out. Given that limitation, it's better to have the water flow separate cleanly from the edge of the propeller hub. The flared edge achieves this separation. We don't want the water mixing with the exhaust directly behind the prop hub. That creates even more drag than the small flare on the hub. You can clearly see the separation between water and exhaust in this video of a prop underwater: czcams.com/video/DDsPag56GQE/video.html In summary, I don't think the flared hub is the best option. But it is the most preferable of the bad options, given that we need to allow the engine exhaust out through the hub.
i have to design with a symmetrical class airfoil for my M/G prop. but i can't even start the design without a real world torque figure for my, as of yet, undeveloped 9-phase.. Min-Kota must have a small fortune behind the 38V user installable salt water number....so i am following their lead on that, and going 12 cell..
Very impressive, whell explained and illustrated. Very intresting, thinking about solution to improve our cabincruisers "planespeed". It's 27 ft, ca 3500kg , 170 hp TD yanmar, staigth shaft drive, 4 blade prop. max out around 17 knots. (Swede so exuse my bad spelling" XD I jusr wonder about "the tube/pipe around" the prop, how to improve it or like the first fast prop bout with screw before the prop or dual prop fix monted even a gear from a duoprop on the shaft? Possible or madness? ; ) ideas?
Legolas Ok : you make no mention of pitch, diameter, cupping, make, rpm design or engine torque peak, in the absence of any real information one can only suggest switching to a 3 blade prop as they are better for top end than a 4. Give us more info and you will get a better answer ....
Nice video. Just subscribed. I was wondering if you have an example of a prop that works as thrust for a 47' sailboat but also as a prop that generates electricity when sailing?
I don't have any specific manufacturers yet, but if you do a search for "yacht electric motor", you can locate manufacturers that supply that. Anyone that makes an electric motor for yacht propulsion often adds in the ability to turn it into a generator. Here are the first two results I found from google (not an endorsement): electroprop.com/sailor-serial-hybrid/ electricyacht.com But that just handles the motor. Then you need the propeller. Biggest point: don't get any feathering or controllable pitch propellers. Otherwise, the generator capability never works. You want a simple fixed pitch propeller. There are some special blade shapes to make sure it works just as well in generator vs propeller mode. But unless you are buy a custom cast propeller, I doubt you will find anyone that makes such a specialized option. Just get the right propeller for propulsion and the generator should work pretty good too.
Sure. I just worked on an ocean construction ship that had two variable pitch propellers, also called a controllable pitch propeller (CPP). The downsides: more expensive than fixed pitch; more machinery that can break; lower efficiency than a fixed pitch (when comparing on equal pitch). So you don't see CPP's on freighters that spend 90% of their time at one speed. But they are handy for ships like ferries, offshore supply vessels, and construction ships. These are all ships that need to work at different speed ranges. Those are the best uses for CPP's.
By keeping the engine speed constant (or mostly constant) you gain efficiency from the engine. Well, if you spend most of your time at 1 speed, you've accomplished the same thing with a regular prop without all the components to go wrong... Navies also like them for their ability to quickly and precisely change speeds. For instance, when a DDG51 class caught the dumbs and almost got run down by me (container ship) he was, by combination of GTS and CPP able to put the power down and escape...
Hello! Thanks for your fantastic video. I have a question. In 5:44, you said the lift is perpendicular to zero lift line is, that true? I couldn't find it in the books. Isn't that supposed to be perpendicular to the relative velocity?
It's in every explanation of lift from airfoil sections. The lift is always at right angles to the zero lift line, no matter what the direction of travel. Lift occurs just after the top of the upper curve of the chord, and is produced by a low pressure area. If you tilt the upper curve away from the direction of travel, the Lift component has to follow the tilt of the ais.
I'm no expert in aircraft wings. But at first guess, nothing would happen. From my understanding, vortex generators on airplane wings exist to ensure reliable turbulent flow over the wing. Propellers operate at a higher Reynolds number than aircraft wings. We are already far into the turbulent flow regime. All the things the vortex generator acocomplishes by design, we achieve as a natural consequence of the propeller operation.
Not sure why you would need them. As a sailing cat, the boat already has rudders, and catamaran means twin engines (usually). That already gives very good control.
@@carlsmith2826 My mistake. I thought you referred to Z-drives which are azimuthing propellers, directly coupled to engines. As to electric powered podded propulsion . . . that is a much longer answer. I'm working on some videos that address this. But the biggest issue I have with electric propulsion for boats less than 30 m. is the challenge of supplying suitable parts. It can be difficult to find an appropriate motor at that size. There are several industrial motors that are suitable. But then it can be difficult to create the power infrastructure to support them. That is a whole complex ship infrastructure problem.
Hello! Do you have any suggestions on litterature for a master in mechanical engineering but novice in Naval Architecture? Preferably in SI units and with regards on the actual hands-on theory rather than the mathematics or differential equations if you know what I mean hehe. Best regards, Christian
The Voith Propeller doesn't experience swirl in the same sense as a conventional propeller. Totally different flow pattern. At slow speeds (below 12-14 knots) the Voith Propeller can be more efficient. The trade-off is greater complexity for the Voith propeller (i.e. increased cost). But Voith also offers increased maneuverability. I really need to create a whole video on Voith propellers.
Can you changes new life craft to a rocket tubes bosster to left up landing on lands installed parachute inpack tubes sky labs..all ships lifet craft not.the.plotting boye big waves higth tide.. Need rocket bosster apolo NASA craft styles ships copen..DSM..
I get confused when marine engineers aircraft 'propellers' as an analogy with ship 'screws'. Don't they differ because an aircraft propeller relies much more on working in a compressible fluid rather than the other non-compressible fluid of a ship's screw?
Propellers are a brute approach to solve what Mother Nature already has found multiple solutions for creating motion from a viscous ambient fluid (air/water). The Wright Brothers understood that and tried to emulate a single one of the elements of bird wing designs, wing-twisting, which our modern rigid-wing airplanes have not yet been able to replicate efficiently. Also note that there are no propellers in nature? HMMM... I think that the Energy Efficiency of propellers ranges from 10 to 35% , vs let's say a dolphin EE, which has been calculated at ABOVE 100% in some cases.... again, HMMMMM .... I wonder if we could do better! YES: The Manta Marine Propulsion System IMO...
Generally, no difference. If your hull is not symmetric, then you may get some benefits of right hand vs left hand, depending on hull shape. (Asymmetric hulls are possible in the individual amas of catamarans and trimarans.) Selecting right hand vs left hand, the largest deciding factor is probably which direction you turn when backing out of the slip at your home marina.
@@DatawaveMarineSolutions Awesome! Your reply including the tail walking in reverse is supper impressive to me (right vs left hand prop). I am not only a hull diver, but also a sailboat owner. This rebuttal gives me much faith that you will help engineers consider marine growth and opposing elements of balance. (5 🌟 reply) *Most power boats with STBD & Port running gear have right hand on STBD side & left hand on port side. The only real difference to me, is the STBD propeller nut often kicks loose when bumping the boat in drive. Using a king nut with a locking set screw will help prevent the propeller nuts from loosening when operating. Standars ABYC jam nut, king nut, cotter pin doesn't always work on vessels with heavy nuts lol.
Not when viewed in the frame of reference of the propeller. With fluid dynamics, we frequently set the frame of reference to the moving object (the propeller centerline). Now the propeller is stationary (but still rotating), and the water moves the opposite direction of thrust.
@@DatawaveMarineSolutions Right, this is based on Blade element theory, where V0 should be the axial flow to the propeller (equal to the advance velocity of propeller < Velocity of Ship) from the frame of reference of the propeller, and hence the direction should be reversed, I think the one which is used in the video is for the propeller in front of the Aeroplane.
It comes down to the difference in density and application. Airplane propellers operate in air, which is roughly 1000x less dense than water. Due to this, the propeller this follows the same basic shape, but with different proportions. It spins faster and uses less surface area. Due to these changes, you also get less skin drag and less induced drag on the propeller, which means better efficiency. Put it another way: because the propeller spins faster, it doesn't need to produce as much force with each rotation. That allows us to focus the airplane propeller on efficiency, rather than fitting sufficient thrust into a relatively small diameter. There are several physics and design decisions that go into that result. But the basic idea that I want to convey: when an engineer designs a propeller for a ship or an airplane, we always try to get the best efficiency, given the design constraints. Normally, ship propellers face the problem of trying to fit too much thrust into too small of an area. In those cases, you need to sacrifice efficiency. Airplane propellers have a little more space to work with, and so it can be easier for those designers to achieve higher efficiency.
The general field is called Naval Architecture and Marine Engineering. A good starting overview is the Wikipedia article. en.m.wikipedia.org/wiki/Naval_architecture
Also important. That was just more detail than I wanted to get into for one video. But I do need to create another video about them. For anyone that wants a quick definition of blade cup: www.mercuryracing.com/prop-school-part-4-blade-cup/ We don't see propeller rake and cup on many commercial vessels. They don't move fast enough. But they are important aspects when designing propellers for high performance boats.
Interesting stuff. In hydropower dams, Francis Turbines get around 93% efficiency in part because they have a "de-swirler" stage at the end. Is there no way to create a propeller/impeller analog of a Francis Turbine to bump up efficiency?
Not easily. We do use de-swirlers of various types on some propellers. The main difference between the Francis Turbine and a propeller is that the Francis Turbine is inside a pipe. The water must go through the turbine. In an open propeller, the water has the option to go around, which significantly alters the possibilities at the propeller. Waterjets would be the closest analog to a Francis Turbine. They do use an impeller in a pipe. But they also have efficiency losses from the inlet suction.
I was told by many unreliable sources lol, that jet drives are less efficient. But I can't help but notice many of the faster vessels on the water are jet drive. Does it take more hp and fuel to accomplish the same speed on equal vessels? (jet vs standard)
I'm not a fan on jet drives left in the water though. Hinkley puts out many boats like this, but ii is near impossible to remove the barnacles from the impeller without a pressure washer wand. (Hull diver perspective) Jet drives should be kept on a boat lift.
Interesting channel. You need to get a better mic, the audio is "Buzzy" and the sound levels are too low. I have to turn my volume up to hear your videos and then turn it back down for others.
Thanks for the tip. The audio level is interesting. I normalize all my audio to -0.5 db. I'll check my video editor to see if it snuck a reduction on me. Can you link another video that you watched for comparison? I'd like to see if the other videos have their audio turned up or if mine is turned down.
I did allot of testing to find the ideal prop for my model aircraft motors.
Convention dictates a certain pitch for modelers to use, most commonly an 8-10 inch per rotation prop is used.
I tested with the 12-8 and found the engine could not drive the prop into the power band of the 2 stroke motors being used, it would stall the engine and less thrust was produced.
My experiments lead me to a larger prop and a shorter pitch. My 10 cc motors could drive a 13-4 wide blade into the 12,000-12,500 rpm range, the motor was happier and the thrust was twice the thrust produced by the 12-8 prop.
It pays to do the testing, never listen to idiots, always do the testing yourself.
I had two props on an old outboard motor many years ago. They were the exact same make, diameter and pitch. One was cupped slightly different and the motor performed noticeably better with one over the other.
Great video, could you do one on impellers and whether they can be more efficient than propellers?
Great idea. I will add it to my list.
I would love to see what DMS would have to say about surface piercing propellers .
It's on my list to create a video about them.
This is really good, thanks for sharing the knowledge!
Excellent Talk, although I clean barnacles & oysters for a living as a hull diver. Alot of the over engineering equals extra growth and extra drag do to marine growth. I am seeing alot more IPS Drives that eliminate bow and stern thrusters and also give the ability for joystick controls. The propeller design seems to come to mind because of this talk. It is a pod drive with forward facing twin propellers rotating opposite one another, forward propeller having three blades and aft propeller having 4 blades. It probably maximizes thrust while countering swirling. This is all just from underwater observation though, no real performance testing by me.
Like to see you do a presentation on the design issues related to the reduction of underwater noise created by vessels.
very clear and well presented
Most people confuse propeller shape - especially the leading edge dimension - with air and low / high pressure of air. Water is incompressible so it is about how a prop redirects water flow around it and thrust is developed by the change of water flow over speed and water pressure after it leaves the propeller. So blunt leading edges are no longer used much anymore.
Very surprised you did not cover gear ratio selections and the importance that props spin slowly ... because fast spinning props cause cavitation at the tip and lose thrust. Another missing element is Blade Area ratio. Very important, and number of blades and blade shape.
To the question below Impellers are not more efficient than propellers, because they are inherently different to propellers, as impellers are part of pumps.
counter rotating props could also be discussed here regarding flow efficiencies.
And speed limitations. For standard propellers max speed is around 37kts in most cases. This can be improved if CCP props are used - also known as variable pitch propellers and for very high speeds props become wedges so they become supercavitating foils and are raised for planing craft so become surface props and are good to very high speeds.
Wow...I new a little bit about it...but that is really complicated...I fully understand now...just don't quiz me on it 😅 thanks....great video..
Three important unmentioned items:
1) Propeller swirl is caused by a propellers inability to draw water into it by gravity equal to the exhaust velocity volume of the propeller . The exhaust volume exactly equals the intake. A delay causes most of the swirl.
2) Marine propellers get the water from the surface. The reason for this is the momentum of water. due to its mass. If not true, a marine propeller would be pulling water from China.
3) Propellers are very sensitive to tip speed. A 20 inch 4 blade propeller with 0 pitch has @ 1000 rpm, a tip speed of 5233 feet/minute, or just under the old "Mile a Minute" rule in engineering. The power needed is 5 HP.. The same 20 inch 4 blade prop with 0 pitch , at 2000 rpm requires 40 HP. This is why reduction gears help with thrust AND SPEED. The optimal diameter/pitch ratio is 12/10 for line pull and 10/12 for speed. This works from a practical standpoint. Usually, for a general purpos boat, a square wheel is optimal.
,All of this information is based on design of several boats and variations in design. Hope it helps someone. Especially hope it helps someone involved in using finite analysis or other digital development software HINT...HINT.
Interesting points. Myself, I believe in scientific tests and hard experiments. It would be really fun to check these concepts. Based on your description, your first point seems to indicate that propeller swirl is due to an interaction with gravity. If that was the case, we could easily create a test rig with the propeller mounter horizontal instead of the conventional vertical. Gravity would be equal across the entire propeller. According to what you described, we should get no swirl in that case.
I can also think of another test for the argument that propellers get their water from the surface. Simply stick the propeller in a pipe and ensure the inlet to the pipe is well below the surface. If the propeller truly gets it water from the surface, eventually, the propeller should run out of water, or the flow through the propeller should just stop.
It would be fun to test.
This is good stuff. As a recreational boater (power, sail, rowing, (as well as a huge fan of land/ice sailing)) I’m hoping you can address some items that pertain to smaller vessels
Thanks for the kind words. Any suggestions of topics you would like me to cover?
Elegant but thorough. Well done.
Is there a factor for the noise the propeller produces? This would be important for a submarine prop design or to protect animals.
Yes, absolutely. I'm not an expert in propeller noise, but some of the basic design principles include:
- always use an odd number of blades to reduce pressure pulses as blades rotate past vertical surfaces. (even number of blades, and two blades align at the same time, doubling the pressure pulse).
- Increase the number of blades to reduce cavitation and general noise from the propeller
- If possible, rotate at slower RPM.
As a boat enthusiast, I find all of your videos interesting and informative... thanks... well presented.
I like the sense of humour of defining the most efficient propeller, as one which has zero angles of attack and no thrust!
Here is a question that one never seems to see the answer to it.
Considering that water is incompressible and the air is compressible, then if we take the same multiblade propeller with a high blade area for comparison, ( even an impeller) what would the velocity/pressure profile of the fluid medium being used ( compressible air or incompressible water) THROUGH THE THICKNESS OF THE PROPELLER BETWEEN THE BLADES. and the immediate zone around the propeller. It is not an easy answer especially for those water propellers where the water velocity changes as it goes through and accelerates through the propeller!!!
As you said, predicting the exact velocity profile is a little difficult (but achievable with modern computers). Interesting, the theory and mathematics behind propellers started with this exact problem. We started with a goal for a velocity and pressure profile and created a device to achieve that. In the zone directly around the propeller blades, we see minimal change in velocity of the fluid. The one exception is the fluid right on the surface of the blades, which accelerates as it passes around the leading edge of the blade. The pressure shows a huge change in the region around the blades. It spikes from a strong negative pressure (suction on the forward face) to a strong positive pressure (pushing on the back face).
This is the key behind propellers. We are trying to create a sharp change in pressure, and the velocity change is just an unfortunate side effect. The velocity of the fluid accelerates as it approaches the propeller and then slowly decelerates far downstream.
@@DatawaveMarineSolutions Thank you for replying. I thought about writing a book on propellers as I do feel that propellers could be misunderstood. I wish to share my philosophy on some types of propellers/ impellers. The philosophy stems from the fact that water is incompressible and it is also non-expandable as we must stay away from cavitation in this discussion. Having a propeller whose blades are very thin and they form what is effectively a multi-start thread on a deeply threaded rod, we can forget about Bernoulli coming into the picture, as there are other features to consider when we know that water is incompressible and non-expandable and is going through a threaded rod where the void spaces remain constant through the threaded rod. If we consider a shrouded impeller, rotating with its helical blades, it is no different from considering a piston moving along a cylinder where it sucks in water from the front and pushes water at the back. WITH SUCH A SITUATION THERE IS NO LINEAR ACCELERATION OF WATER IN BETWEEN THE BLADES OF THE IMPELLER AND SO NO FORCES ARE PRODUCED IN THE SPACE OF THE IMPELLER. However, the non-expandable water at the front of the impeller will cause a sudden suction and the lower pressure than ambient will accelerate water ahead of the impeller. At the other pushing end, the pressure is higher than ambient and so water will pass through the blades at constant velocity but at the pushing end, the water will be accelerated. Hence the propulsion forces are not produced in between the blades of a helical propeller but much ahead and much behind the propeller.
All this is due to the fact that we are assuming perfect helical blades and incompressible and nonexpandable water going through. Note any threaded nut is very happy going along a rotating threaded rod, does not increase nor decrease its volume and hence that is the condition of such a water propeller or an impeller we are considering. The forces in a propeller are generated only where there is the acceleration of water and there is none in between the space of a helical propeller but there is plenty of acceleration in the zone before and after the propeller.
Now if the blades are not perfectly helical ( really constant pitch) but are curved to diffuse convergently or divergently as in the case of a jet compressor stage, where the exit velocity is different from the incoming velocity, then the volume of water passing in between the blades acting as a diffuser will have to change the area it passes through and so for a curved blade that does not follow a perfect helix, a shrouded propeller should have the exit area of smaller area than the intake. If we assume that the incoming water into the propeller v, has doubled its velocity to 2v at the exit, due to the curve of the blades, then there is an acceleration of water in between the blades of a propeller, and propulsion forces are generated in between the blades of the propeller. Note that in this case we still do not need Bernoulli and aerodynamic sections as it is all a case of changing the momentum through the blades in this case.
Now let us talk about surface propellors, as the manner in which they operate efficiently, is related to what was said above. Now water may be incompressible but it will shatter into small drops if it is accelerated heavily and suddenly. If a paddle hits the surface of the water, the sudden effect will put a lot of force on the paddle but only a few drops of spray will shatter around the space where the water was hit.
This is no manner in which to accelerate water either by sudden suction or a sudden pressure as water will show other characteristics. If water was like solid steel balls which do not compress not expand, then all that was said above will still apply but water is not like that, IT CANNOT BE ACCELERATED SUDDENLY. This is the importance of arranging for the apparent entry into the blades to be parallel with the leading edge so that the surface propellor will not just hit the lump of water, but it will load it onto the leading edge of the blade and coax it to accelerate along the blade due to the curve of the blade, and as the lump of mass of water reaches the trailing edge it is released with high velocity and there is no more acceleration behind nor before the surface propeller. It is interesting that the solidity of the water in a surface propeller can change it shape due to the rheology of the water and all that acceleration along the blade must be done smoothly and fairly quickly before the lump of mass of water changes shape in smaller spray with no effective mass to drive!.
So my point of discussion is between the two limits of a fully immersed propeller with perfectly helical thin blades where the space between the blades does not change and so there is constant velocity, no accelratio0n but a great pressure change between the intake and the exit., and all the propulsion acceleration forces in such a helical propeller will take place totally ahead and behind the propeller. Such a propeller can be enclosed in a parallel cylindrical shroud.
Then there is the non-helical curved blade propeller which accelerates the water along with the blades and hence the output area will have to be less than the entry area. For such a propeller with a slip of 50%, it is interesting how small the curve in the blade should be.
With surface propellers introducing the air which is incompressible and expandible, then the lumps of masses of water can be separated and that is the reason the surface blade is curved as it is as water is no longer compressible and non-expandable and it can also roll off the blades if the acceleration on the lumps of water is too slow, on the other hand, one just cannot hit a lump of water suddenly as it breaks into small drops and so THE SMOOTH ACCELERATION OR CHANGE IN VELOCITY ON THE BLADES OF A SURFACE PROPELLER MUST BE SMOOTH TO RETAIN LARGE ENOUGH LUMPS OF WATER BEING ACCELERATED ON THE BLADES TO FINISH UP WITH ENOUGH DRIVING FORCES.
In my book, I think I would cover the effect of aeration and cavitation on, the helical propeller along which there is no acceleration, the curved blade propeller along which there is acceleration, and Bernoulli and the air propellers will show the misgivings we all know about.
However, for now, I want to delve into the situation that even if the velocity of the water in between the blades of a propeller remains constant and the blades are purely very thin helical blades, shrouded in a cylinder in order to avoid water escaping or incoming through the surface of the shroud, one can have a good propulsion drive without thinking too much on the NASA and Eppler and other cross-section which their variation is velocities and pressures along the surface of the blade. The nature in which the accelerations of water are handled is very important and in surface drives, it is not a case of hitting a lump of water with a cricket bat! It is interesting to start looking at drops of water, as stell ballbearing which does not change shape in all the transactions we activate in propellers, or else as rubber balls where the bat/blade hitting the water drop could change its shape as do most surface propellers as there is air introduced to do the buffering, The fact that it is all inertia, acceleration and the rheology of the water, it makes it all so interesting to understand propellers in a better fashion.
If we had to add a nozzle ( diffuser) at the back of a propeller then one needs to build up pressure and one cannot use a propeller with narrow blades as found on an aircraft but one with multiple close blades as in a jet compressor where the high pressure built up cannot escape back through the blades as in a helicopter top rotor or indeed any wing with spaces ahead or behind the edges. Nozzles, are really velocity/pressure modifiers" amplifiers" with no moving parts and are related to diffusers, where high pressure can be changed to high velocity or high velocities can be changed to higher pressures. In ships, we need not worry too much about how it all works, as the modern jet engine says it all, for after all, in a jet engine, what happens between the blades is all that happens in a ramjet due to the fact that it uses compressible fluid like air. A jet engine is really a lot of ramjets in parallel made to rotate to be able to work when the engine is stationary on the ground! The fact that water is incompressible and on occasions boils, so expandible, we need to fully understand what happens in between those water blades with the convergent and divergent diffus4ers that may exist before, through, and behind the propeller. Perhaps understanding diffusers are a better investment than understanding propeller blades on their own. We could have a front diffuser, a hot chamber to boil the water, rather than a propeller and a rear diffuser and the whole engine would be located in the propeller!!!!!! Pity that water is so difficult to work with and its latent heat of boiling it takes too much time relative to it passing between the blades of the propeller. Now that would be a difficult machine/propeller to calculate mathematically !!!
Thank you for listening,
@08:21 is a Grim's Vane Wheel, which vanes freely on the shaft in the propeller's propwash. Its blade sections within the driving prop's radii are formed to act like a turbine while the vane wheel's sections at the remaining radii towards its blade tips exceeding the prop's diameter are formed to act like a second prop in the wake of the main prop. That gives the vane wheel's blades a bizarr looking warp.
Unfortunately, those Grim Vane Wheels didn't really succeed (e.g. their unnoticed loss during their first operation on QE2 after her big propulsion retrofit at the Lloyd Yard at Bremerhaven), and their application remained sporadic to mainly research vessels (e.g. hydrographic RV GAUSS) and a few container vessels from rhe Bremer Vulkan yard that were built in the mid 80s within ship research projects that were partly funded by the government.
The same goes for those wake equalizing fins and ducts (e.g. Schneekluth and Grothues-Spork) that were shown a few frames earlier in the video, and which where sporadically applied on other container vessels from the Bremer Vulkan in the same era.
P.S. Just found this reprint from HANSA on Schnekluth WED
www.schneekluth.com/wp-content/uploads/2019/03/hansa-about_wed.pdf
P.P.S. Here another article about the Schneekluth WED
(n.b. of course one should be wary about the promised efficiency gains vs. extra costs and risks; of course ship operators asses the latter a bit differently from their or others' experience)
www.schneekluth.com/wp-content/uploads/2019/03/brochure_english.pdf
P.P.P.S. Here's a paper by a researcher from the Potsdam Ship Model Basin about wake influencing devices.
www.marinepropulsors.com/proceedings/2011/WA3-1_Heinke.pdf
P.P.P.P.S. Here are some slides from a talk that gives an overview of propulsion efficiency improving measures by two researchers of the Dutch MARIN ship model towing tank.
www.stg-online.org/onTEAM/shipefficiency/programm/PPTdeJong.pdf
I recently saw research at NASA Ames regarding the 'PRANDL wing'. Apparently all wing designs are descended in some way from Prandl's mathematical work of 1925, which established the most efficient wing for a given length. But his 1933 paper demonstrated that wasn't the whole story. The most efficient wing without that constraint is longer and has a very different shape. One of the benefits in an aero application is that the tip vortex disappears. These wings have been shown to be substantially more efficient, as well as quieter, and with the replacement of adverse yaw with proverse yaw they eliminate the need for a tail plane, further increasing efficiency. The efficiency has been shown at NASA to also extend to propeller blade shapes.
I'd like to see how this applies to boat and ship propellers.
The "duo props" developed by Volvo claim to have a 30% improvement in effectiveness, 30% more speed at the rpm you normally use. If you get 15 knots at 1800 rpm, by using a duo prop you effectively get 19.5 knots at 1800 rpm.
That is the claim at least. There must be something to it though, since cruise ships and ice breakers have started using the system on pods. They wouldn't put them on a cruise ship if they didn't give a measurable benefit to ship operation.
Many European based yacht builders have started offering Volvo-Penta pod driven option, which does come with the duo prop. With the twin pods in the back, a bow thruster and the application installed in the controls, push a button on the controls and you have dynamic positioning operating.
Would a ducted propeller be more efficient and use the swirl too?
Would make a better skin, like shark or a golfball, the propeller more efficient?
Does the number of wings rise efficiency?
Are the effects in air and water same or is there other things to consider then density?
I wish I had a physics teacher like you in high school.
Hi Andreas. Excellent questions. I'll give you the short answers.
Would a ducted propeller be more efficient and use the swirl too?
Ducted propellers are more efficient, but not because of the swirl. I need to do a whole video those. A propeller duct is basically a wing wrapped around the propeller. As the water gets sucked into the propeller, it runs over the duct wing and produces extra lift. But we also have extra drag from pulling that duct through the water. The benefits outweigh the drag problem up to a certain speed (around 14 - 18 knots). Then it becomes less efficient.
Would make a better skin, like shark or a golfball, the propeller more efficient?
It might help some. But only about 2-5% The skin friction on the surface of the blade is a minor part of the total blade drag. We actually get a lot of drag from the lift generated by each blade. (Physics: you can't get anything for free.) Some experiments have examined using those surface textures to improve the lift on the blade. With the right texture, we can keep the water flow attached to the blade surface and use a more aggressive blade shape. But more aggressive is not more efficient. All those interactions are hard to gauge. Normally, we have to just build a model and run an experiment to see what happens.
Does the number of wings rise efficiency?
Generally, yes. Many of the efficiency penalties depend on how much force we try to squeeze into each blade. More blades / wings means less effort from each blade and better efficiency.
Are the effects in air and water same or is there other things to consider then density?
Air and water are largely the same, aside from the density. Just three major differences:
1.) Air and water propellers generally run at different speeds.
2.) In water, we also need to worry about the limits of cavitation. czcams.com/video/MyZzhwYMytc/video.html That forms an upper limit to how much thrust we can fit in each blade.
3.) In air, we also worry about compressibility. Air is compressible. It's density changes depending on the pressure. This is how we get sonic booms at the speed of 343 m/s. But even before you hit the sonic boom speed, the air compresses some and we need to adjust the design for it.
Great questions.
@@DatawaveMarineSolutions Interesting about the blade number, and as always I understand optimization is done with regards to some variables while leaving other variables fixed. My follow up question about your statement that: more blades leads to better efficiency, would be: is that when fixing the required thrust per blade or in general? Say i would like a certain low speed from a small displacing vessel well below hull speed. The free/undisturbed stream and the propeller diameter are both fixed. Would more propeller blades still be beneficial over fewer when the propeller thrust requirement is constant? Best regards, Christian
Don't forget about barnacles & oysters. Stuff grows underwater. Unless your designing outboard propeller, I believe simple is better 😉 (hull diver perspective)
I’ve heard of cupping the blades for efficiency, but has anyone done more on blade designs away from the tip and more at the leading and trailing ends to increase efficiency and reduce noise?
Why do propeller hubs, at least for outboard motors, usually widen at the back end? I would think that it would create extra drag.
That is an excellent question. I can only partially answer it. I know a few professionals that work in small boat prop design, and I suspect they know some secrets about optimizing performance at the propeller hub.
That said, I suspect the flare on the hub has a lot to do with the engine exhaust. Most outboards route their exhaust flow through the propeller hub. So we can't put a tapered hub on there. We need an open hub to let the exhaust out. Given that limitation, it's better to have the water flow separate cleanly from the edge of the propeller hub. The flared edge achieves this separation. We don't want the water mixing with the exhaust directly behind the prop hub. That creates even more drag than the small flare on the hub. You can clearly see the separation between water and exhaust in this video of a prop underwater:
czcams.com/video/DDsPag56GQE/video.html
In summary, I don't think the flared hub is the best option. But it is the most preferable of the bad options, given that we need to allow the engine exhaust out through the hub.
i have to design with a symmetrical class airfoil for my M/G prop.
but i can't even start the design without a real world torque figure for my, as of yet, undeveloped 9-phase..
Min-Kota must have a small fortune behind the 38V user installable salt water number....so i am following their lead on that, and going 12 cell..
Very impressive, whell explained and illustrated. Very intresting, thinking about solution to improve our cabincruisers "planespeed". It's 27 ft, ca 3500kg , 170 hp TD yanmar, staigth shaft drive, 4 blade prop. max out around 17 knots. (Swede so exuse my bad spelling" XD
I jusr wonder about "the tube/pipe around" the prop, how to improve it or like the first fast prop bout with screw before the prop or dual prop fix monted even a gear from a duoprop on the shaft? Possible or madness? ; ) ideas?
Legolas Ok : you make no mention of pitch, diameter, cupping, make, rpm design or engine torque peak, in the absence of any real information one can only suggest switching to a 3 blade prop as they are better for top end than a 4. Give us more info and you will get a better answer ....
Your so Swede!!!
Nice video. Just subscribed. I was wondering if you have an example of a prop that works as thrust for a 47' sailboat but also as a prop that generates electricity when sailing?
I don't have any specific manufacturers yet, but if you do a search for "yacht electric motor", you can locate manufacturers that supply that. Anyone that makes an electric motor for yacht propulsion often adds in the ability to turn it into a generator. Here are the first two results I found from google (not an endorsement):
electroprop.com/sailor-serial-hybrid/
electricyacht.com
But that just handles the motor. Then you need the propeller. Biggest point: don't get any feathering or controllable pitch propellers. Otherwise, the generator capability never works. You want a simple fixed pitch propeller. There are some special blade shapes to make sure it works just as well in generator vs propeller mode. But unless you are buy a custom cast propeller, I doubt you will find anyone that makes such a specialized option. Just get the right propeller for propulsion and the generator should work pretty good too.
the displacement figures of different types of aircraft carriers we find on Wikipedia, are they of fully loaded aircraft carriers or empty???
I suspect they are close to fully loaded. But if I were a military, I would introduce some ambiguity in those public figures.
Great videos :D thanks
Do variable pitch propellers work on large seagoing vessels?
Sure. I just worked on an ocean construction ship that had two variable pitch propellers, also called a controllable pitch propeller (CPP). The downsides: more expensive than fixed pitch; more machinery that can break; lower efficiency than a fixed pitch (when comparing on equal pitch). So you don't see CPP's on freighters that spend 90% of their time at one speed. But they are handy for ships like ferries, offshore supply vessels, and construction ships. These are all ships that need to work at different speed ranges. Those are the best uses for CPP's.
By keeping the engine speed constant (or mostly constant) you gain efficiency from the engine. Well, if you spend most of your time at 1 speed, you've accomplished the same thing with a regular prop without all the components to go wrong...
Navies also like them for their ability to quickly and precisely change speeds. For instance, when a DDG51 class caught the dumbs and almost got run down by me (container ship) he was, by combination of GTS and CPP able to put the power down and escape...
Thank you guys for actually responding to my comment!! It really helps!!!
If so then why aeroplane propeller blades are thinner than boat propeller blades even though water offers more friction than air.
Great video!
very nice video
You didn't mention cavitation which poses a considerable influence on marine propeller design.
See the other DMS video on cavitation: czcams.com/video/MyZzhwYMytc/video.html
Hello! Thanks for your fantastic video. I have a question. In 5:44, you said the lift is perpendicular to zero lift line is, that true? I couldn't find it in the books. Isn't that supposed to be perpendicular to the relative velocity?
It's in every explanation of lift from airfoil sections. The lift is always at right angles to the zero lift line, no matter what the direction of travel.
Lift occurs just after the top of the upper curve of the chord, and is produced by a low pressure area. If you tilt the upper curve away from the direction of travel, the Lift component has to follow the tilt of the ais.
Have you investigated the Sharrow propeller design
Actually, I work with Sharrow Marine. I haven't done a review on them because it could potentially be biased.
What would happen if you use vortex generators like that on a aircraft wing ?
I'm no expert in aircraft wings. But at first guess, nothing would happen. From my understanding, vortex generators on airplane wings exist to ensure reliable turbulent flow over the wing. Propellers operate at a higher Reynolds number than aircraft wings. We are already far into the turbulent flow regime. All the things the vortex generator acocomplishes by design, we achieve as a natural consequence of the propeller operation.
Y the marine propeller blade rake is towards rudder side ?
Though its hub doesn't look like, it must be a CPP with blades in reverse pitch.
Nick what is your thoughts about Z-drive pods attached to a sailing catamaran?
Not sure why you would need them. As a sailing cat, the boat already has rudders, and catamaran means twin engines (usually). That already gives very good control.
@@DatawaveMarineSolutions I was thinking that installing electric motor ones for when you need to motor instead of sail.
@@carlsmith2826 My mistake. I thought you referred to Z-drives which are azimuthing propellers, directly coupled to engines. As to electric powered podded propulsion . . . that is a much longer answer. I'm working on some videos that address this. But the biggest issue I have with electric propulsion for boats less than 30 m. is the challenge of supplying suitable parts. It can be difficult to find an appropriate motor at that size. There are several industrial motors that are suitable. But then it can be difficult to create the power infrastructure to support them. That is a whole complex ship infrastructure problem.
So we don't actually want to use an Axiom propeller on a Mangusta 130
Damn, This is awesome!!!
Hello! Do you have any suggestions on litterature for a master in mechanical engineering but novice in Naval Architecture? Preferably in SI units and with regards on the actual hands-on theory rather than the mathematics or differential equations if you know what I mean hehe. Best regards, Christian
Try this for a start: www.marineinsight.com/naval-architecture/what-is-naval-architecture/
What about swirl with the Voith type of propellor?
Is it more efficient than conventional types of propellor?
The Voith Propeller doesn't experience swirl in the same sense as a conventional propeller. Totally different flow pattern. At slow speeds (below 12-14 knots) the Voith Propeller can be more efficient. The trade-off is greater complexity for the Voith propeller (i.e. increased cost). But Voith also offers increased maneuverability. I really need to create a whole video on Voith propellers.
Can you changes new life craft to a rocket tubes bosster to left up landing on lands installed parachute inpack tubes sky labs..all ships lifet craft not.the.plotting boye big waves higth tide.. Need rocket bosster apolo NASA craft styles ships copen..DSM..
I get confused when marine engineers aircraft 'propellers' as an analogy with ship 'screws'. Don't they differ because an aircraft propeller relies much more on working in a compressible fluid rather than the other non-compressible fluid of a ship's screw?
Geoff Buck The principle is the same, it's just the mass that needs to be different, low mass for gas, high mass / high strength for fluids.
What about kort nozzles.
thank you
i went and downloaded books. i am building an efoil thruster
Perhaps a more accurate title for this video would be: Propeller Engineering Considerations.
Why ship propellers are not designed like an areoplane propellers
May I send you a propeller design to get your thoughts?
Certainly. Consulting work is my primary business. You can send an email to sales@dmsonline.us to discuss a paid consulting project.
Propellers are a brute approach to solve what Mother Nature already has found multiple solutions for creating motion from a viscous ambient fluid (air/water). The Wright Brothers understood that and tried to emulate a single one of the elements of bird wing designs, wing-twisting, which our modern rigid-wing airplanes have not yet been able to replicate efficiently. Also note that there are no propellers in nature? HMMM... I think that the Energy Efficiency of propellers ranges from 10 to 35% , vs let's say a dolphin EE, which has been calculated at ABOVE 100% in some cases.... again, HMMMMM .... I wonder if we could do better! YES: The Manta Marine Propulsion System IMO...
So like fish, it'd seem that a motor that could propels a boat with a swimming action rather than a spinning prop. Very interesting.
how does a vertically rotating paddle steamer paddle compare to a propellor for efficiency?
which rotation works better right hand or left hand
Generally, no difference. If your hull is not symmetric, then you may get some benefits of right hand vs left hand, depending on hull shape. (Asymmetric hulls are possible in the individual amas of catamarans and trimarans.) Selecting right hand vs left hand, the largest deciding factor is probably which direction you turn when backing out of the slip at your home marina.
@@DatawaveMarineSolutions Awesome! Your reply including the tail walking in reverse is supper impressive to me (right vs left hand prop). I am not only a hull diver, but also a sailboat owner. This rebuttal gives me much faith that you will help engineers consider marine growth and opposing elements of balance. (5 🌟 reply)
*Most power boats with STBD & Port running gear have right hand on STBD side & left hand on port side. The only real difference to me, is the STBD propeller nut often kicks loose when bumping the boat in drive. Using a king nut with a locking set screw will help prevent the propeller nuts from loosening when operating. Standars ABYC jam nut, king nut, cotter pin doesn't always work on vessels with heavy nuts lol.
Ship forward velocity and thrust should be in same direction.
Not when viewed in the frame of reference of the propeller. With fluid dynamics, we frequently set the frame of reference to the moving object (the propeller centerline). Now the propeller is stationary (but still rotating), and the water moves the opposite direction of thrust.
@@DatawaveMarineSolutions Right, this is based on Blade element theory, where V0 should be the axial flow to the propeller (equal to the advance velocity of propeller < Velocity of Ship) from the frame of reference of the propeller, and hence the direction should be reversed, I think the one which is used in the video is for the propeller in front of the Aeroplane.
why is an airplane propeller more efficient with less blade area ?
It comes down to the difference in density and application. Airplane propellers operate in air, which is roughly 1000x less dense than water. Due to this, the propeller this follows the same basic shape, but with different proportions. It spins faster and uses less surface area. Due to these changes, you also get less skin drag and less induced drag on the propeller, which means better efficiency.
Put it another way: because the propeller spins faster, it doesn't need to produce as much force with each rotation. That allows us to focus the airplane propeller on efficiency, rather than fitting sufficient thrust into a relatively small diameter.
There are several physics and design decisions that go into that result. But the basic idea that I want to convey: when an engineer designs a propeller for a ship or an airplane, we always try to get the best efficiency, given the design constraints. Normally, ship propellers face the problem of trying to fit too much thrust into too small of an area. In those cases, you need to sacrifice efficiency. Airplane propellers have a little more space to work with, and so it can be easier for those designers to achieve higher efficiency.
Good day can you tell me what line of study is this
The general field is called Naval Architecture and Marine Engineering. A good starting overview is the Wikipedia article. en.m.wikipedia.org/wiki/Naval_architecture
So what about blade rake and cup?
Also important. That was just more detail than I wanted to get into for one video. But I do need to create another video about them. For anyone that wants a quick definition of blade cup: www.mercuryracing.com/prop-school-part-4-blade-cup/
We don't see propeller rake and cup on many commercial vessels. They don't move fast enough. But they are important aspects when designing propellers for high performance boats.
5-10 degrees? This doesn't have much to do with recreational uses, obviously. Interesting nonetheless
Interesting stuff. In hydropower dams, Francis Turbines get around 93% efficiency in part because they have a "de-swirler" stage at the end. Is there no way to create a propeller/impeller analog of a Francis Turbine to bump up efficiency?
Not easily. We do use de-swirlers of various types on some propellers. The main difference between the Francis Turbine and a propeller is that the Francis Turbine is inside a pipe. The water must go through the turbine. In an open propeller, the water has the option to go around, which significantly alters the possibilities at the propeller. Waterjets would be the closest analog to a Francis Turbine. They do use an impeller in a pipe. But they also have efficiency losses from the inlet suction.
I was told by many unreliable sources lol, that jet drives are less efficient. But I can't help but notice many of the faster vessels on the water are jet drive. Does it take more hp and fuel to accomplish the same speed on equal vessels? (jet vs standard)
I'm not a fan on jet drives left in the water though. Hinkley puts out many boats like this, but ii is near impossible to remove the barnacles from the impeller without a pressure washer wand. (Hull diver perspective) Jet drives should be kept on a boat lift.
Very good video but the background music is very irritating.
Agreed. I experimented with background music on one set of videos. It didn't go well, and I have not used background music since.
@@DatawaveMarineSolutions Ah, that's why I didn't notice it on you other videos. I really like the channel by the way.
@@DatawaveMarineSolutions I actually really like this background music. What is the name of this song?
cooooool
Interesting channel. You need to get a better mic, the audio is "Buzzy" and the sound levels are too low. I have to turn my volume up to hear your videos and then turn it back down for others.
Thanks for the tip. The audio level is interesting. I normalize all my audio to -0.5 db. I'll check my video editor to see if it snuck a reduction on me. Can you link another video that you watched for comparison? I'd like to see if the other videos have their audio turned up or if mine is turned down.
Advertisements are the best guide, they're pros, they get it right.
Ask the Royal Navy about thier Astute class submarine propellers for excellent state of the art knowledge haha (-:
why a crystal around your neck?
Just in case engineering and science fail?
would be detter with out the drama
…key control >> vortex control
Here's a prop that combines standard props with a centrifugal compressor.
drive.google.com/file/d/0B_C2fU77zYjUazM5S192aGRfZ0k/view?usp=sharing
PWD: BAT
Efficiency-optimum-performance
🤷♂️
Bill Nye the science guy
this video is simultaneously awesome (information) and super cringe lol
Agreed. I experimented with a few different presentation techniques on this video. Several things that I learned to never do again.
@@DatawaveMarineSolutions I like your content I was just being a smart ass! keep up the good work.
Sssstts
Just give the facts, don't act like your audience is 5, it degrades the video